Illumination without HDRI (cycles)
The problem with your question is that you are erroneously thinking that there are areas with lights and some without in a JPEG or other display referred image.

In reality, every single pixel is an emitter of light. As you may guess, with all of the crazy math involved in a ray tracing engine, all of that light ends up with a very complex interaction series in any image. This means that it is impossible to simulate real-world lighting without using some form of IBL.

Worse still, a JPEG is what is known as a display referred image. That is, the encoding of the image takes all of the data of a scene and maps it into the display referred range of 0.0 to 1.0. During this transition, you are losing a tremendous amount of the information in a scene.

The most ideal format for IBL is of course EXR[1]. This format permits storage of scene referred values from zero to infinity, which helps to encompass the complexity of most captured scenes.

[1] For those interested in the nerd stuff behind this statement, there is a great discussion of encoding quantization here.